(2) The formula(a,b)⁢(c,d)=(a⁢c,b⁢d,(a+b)⁢(c+d))abcdacbdabcd(a,\,b)(c,\,d)=(ac,\,bd,\,(a+b)(c+d)) for multiplying ideals of RRR is valid always when at least one of the elements aaa, bbb, ccc, ddd of RRR is not zero-divisor.